Characterization of Plastics Using Mass Spectral Reference Libraries Developed From Pyrolysis-APGC-QToF MS

Significance of the Topic

Understanding the chemical composition of polymeric materials is crucial in quality control, regulatory compliance and material development. Traditional pyrolysis-GC with electron ionization often produces extensive fragmentation and lacks comprehensive spectral libraries, limiting reliable identification. The integration of soft ionization and high-resolution mass spectrometry expands the analytical capabilities and enables the creation of customized spectral libraries to improve confidence in polymer analysis.

Objectives and Study Overview

This application note evaluates two analytical platforms for building and searching in-house spectral libraries of polymer pyrolysates:

• Pyrolysis-GC with electron ionization coupled to triple quadrupole mass spectrometry (py-GC-EI-TQMS)
• Pyrolysis-GC with atmospheric pressure chemical ionization and quadrupole time-of-flight high-resolution mass spectrometry (py-APGC-QToF MS)

The goal is to compare library search performance for common plastics and biobased polymers and demonstrate the utility of soft ionization in enhancing molecular ion detection.

Instrumental Setup

The study employs the following instrumentation:

• CDS 5000 pyrolyzer for rapid, reproducible polymer degradation (310 °C to 750 °C at 20 °C/ms)
• Gas chromatograph equipped with an Rtx-5MS column (30 m × 0.25 mm × 0.25 µm) and temperature program from 45 °C (5 min) to 300 °C at 20 °C/min
• Xevo TQ-GC mass spectrometer in electron ionization mode (70 eV) for conventional library creation
• Xevo G2-XS QTof system with APGC soft ionization and MSE acquisition for accurate mass measurement of precursor and fragment ions
• Data processing and library management conducted in MassLynx 4.2 using a NIST-compatible platform

Key Results and Discussion

Spectral libraries were built from averaged pyrolysate spectra of pure polymer standards. Real-world samples were then screened under identical conditions and searched against the in-house libraries.

• Recycled PET container:
  • py-GC-EI-TQMS forward/reverse match scores: 865/865
  • py-APGC-QToF MS forward/reverse match scores: 818/818
• Biobased PLA straw:
  • py-GC-EI-TQMS match scores: 863/868
  • py-APGC-QToF MS match scores: 851/852

Both platforms delivered robust identification scores (>800), confirming that soft ionization can achieve comparable matching performance while providing molecular ion data for improved elemental composition confirmation.

Method Benefits and Practical Applications

• Soft ionization preserves molecular ions, facilitating accurate mass determination and structural elucidation.
• High-resolution QToF acquisition in MSE mode captures precursor and fragment ions simultaneously.
• Custom in-house libraries enable targeted identification of polymers, additives and contaminants.
• Approach supports rapid screening in QA/QC laboratories and polymer research settings.

Future Trends and Possible Applications

As spectral libraries expand to cover a broader range of polymers, additives and degradation products, automated library searching will become more powerful. Integration with machine learning algorithms could further enhance identification accuracy. The combination of soft ionization, high-resolution MS and robust data processing may also be applied to microplastic analysis and environmental monitoring.

Conclusion

The study demonstrates that py-GC-EI-MS and py-APGC-QToF MS can both generate high-quality in-house spectral libraries for polymer identification. Soft ionization in the APGC-QToF platform offers additional molecular ion information, increasing confidence in compound assignments. These methods provide flexible, reliable tools for polymer characterization in research and industrial laboratories.

References

1. Suge S., Ohtani H., Watanabe C. Pyrolysis-GC/MS Data Book of Synthetic Polymers. 2011.
2. Peacock P.M., McEwen C.N. Mass Spectrometry of Synthetic Polymers. Anal. Chem. 2006;78(12):3957–3964.
3. Sanig R., Cojocariu C., Jones R. Pyrolysis-gas chromatography-high resolution mass spectrometry with soft ionization for increased confidence for polymer characterization. Waters Application Note 720007599, April 2022.
4. NIST/EPA/NIH Mass Spectral Library Compound Scoring: Match Factor, Reverse Match Factor, and Probability. Jordi Labs.